The field of the invention is electronic musical instruments.
The essential elements of a MOSFET chopper keyer system are shown in U.S. Pat. No. 3,636,231, assigned to the assignee of the present invention. As shown in that patent in an exemplary embodiment, each of nine (9) different footages or harmonics at desired amplitude settings, determined by adjustment of drawbar supply voltages, are keyed by separate MOSFET keyer circuits for each of sixty-one (61) keys. Each keyer circuit also has a modulated signal source input such as a square wave and a playing key input which couples the chopped drawbar input to the keyer circuit output when the playing key is depressed. The outputs of the keyer circuits are grouped by similar frequencies usually within one octave and collectively coupled to sine wave, or band pass, filters and eventually to an audio output system and speaker.
In such MOSFET chopper keyer systems percussion for played notes has been provided by pulsing the drawbar supply voltage on suddenly for a particular harmonic and decaying at a less rapid rate, with the signal output coming from the frequency grouped terminals. This causes the percussion which is added to be animated if the sine wave outputs are animated, which can be an undesirable effect. Alternatively, an entirely separate set of keyer circuits may be utilized for one or more footages, for example, in order to produce a separate channel of percussion which would not be animated. This approach entails the additional cost for the separate keyer circuitry.